The field of the invention pertains to external secondary locking mechanisms to prevent the relative rotation and loosening of various separable connectors, most commonly threaded connectors. In particular, the invention is directed to the locking of connectors that join tubes, hoses and wiring together or to an accessory unit. The requirements for aerospace applications are particularly stringent, in particular, for use on engines, hydraulic systems, fuel systems and electric cable connectors.
The current and most common means for secondary locking of aerospace connectors are lock wire and safety wire which require special features be incorporated in the connectors. Other means comprise crimp nuts, fibre nuts and tab washers. These external locking devices may permit some small relative rotation of the connector and usually are destroyed or rendered non-reusable in aerospace applications once unlocked to open the connector.
Two early patents, U.S. Pat. No. 315,895 and U.S. Pat. No. 408,320, each disclose a capture device for hexagonal exterior pipe fittings. The latter capture device completely surrounds the fitting requiring that the capture device be slipped over the adjacent pipe of an open connector before closing the connector and sliding the capture device in place. To remove and replace the capture device, the connector must also be fully opened. The former capture device includes a slot for laterally sliding the device into position to engage the two hexagonal exterior surfaces. Both capture devices require that the exterior hexagonal surfaces be aligned for proper engagement.
U.S. Pat. No. 3,881,753 and U.S. Pat. No. 3,945,669 each disclose a capture device in the form of an elongated clip. The elongated clip is open to permit installation on and removal from a connector without opening the connector. This clip also is applicable to both hexagonal and circular exterior connectors, the clip being formed to a specific axial operating length. Thus, the axial length of the connector is critical to the proper operation of the capture device. Relying on axial length, these clips would not be suitable for threaded high pressure connectors.
U.S. Pat. No. 4,422,675 discloses a capture device that completely encloses and seals about a fuel connector to catch any inadvertent leakage from the connector. The capture device is in the form of a sleeve that includes indentations to engage an exterior hexagonal surface on the fuel connector. The indentations form a full hexagon in one embodiment. In the other embodiment the indentations only engage some hexagonal surfaces on the connector and other indentations prevent axial movement of the capture device.
British Patent Specification No. 624,386 discloses full hexagonal tubes to lock together coupling and nut connection combinations where the coupling and nut are both of the same circumference. Also disclosed is a wavy or serrated tube to accommodate misalignment of the flats on the coupling and nut. A tab in one embodiment prevents axial movement of the tube from a closed connector. As above with capture devices that fully surround the connector, the capture devices of this specification can not be added or removed from a closed connector.
British Patent Specification No. 859,598 discloses a semi-hexagonal spring band to prevent relative movement of a hexagonal coupling and nut connector. A portion of the center of the band is displaced to prevent axial movement of the installed band. The form of the band requires that the coupling and nut flats be aligned and the coupling and nut not be tightened closer than the axial width of the displaced portion of the spring band.